After the accident, when you go to the area where there is a scientist sitting on the floor and another is comforting him, enable the /impulse 101 code. When the man that is sitting down is talking, pound the standing man with your crowbar until he dies. When the old man is done talking, the dead man will talk to you.
After completing the first part and all of the destruction starts, you will be in a room where two scientists let you into the machine that you put the sample in. If they are dead, then this trick will work -- it is after the accident, and not before. Enable the /impulse 101 code and use the eye scanner that is lop sided, next to the door. Go through when it allows you to and you should see a scientist giving Barney CPR. Use any weapon, preferably the crowbar, and hit Barney. He will talk even though he is dead on the ground.
Kill A Barney or Scientist. If the body does not disappear, crouch next to it. Press USE and the Barney/Scientist should talk.